Improvement in solar chronometers



L. MIFFLIN.

Sun Dial.

Patented May 21. 1867.

MFETERS. PHOTO strut 'ffirr.

LLOYD MIFFLIN, OF GERMANTOWN,- PENNSYLVANIA.

Letters Patent No. 64,892, dated May 21, 1867- IMPROVEMENT IN SOLAR GHRONOMETERS.

TO ALL WHOM IT MAY CONCERN:

Bo it known that I, L. MIFFLIN, ofGerma-ntown, Philadelphia, in the county of Philadelphia, and State of Pennsylvania, have invented an Equating Solar Ghronometer; and I do hereby declare that the following is a full,clear, and exact description thereof, which will enable others skilled in the art to make and use the same, reference being had to the accompanying drawings, forming part of this specification, in which- Figure 1 is .a perspective view of the chronometer. I

Figures 2 and 3 views of the gnomon attached to the chronometer; and

Figure 4, plan showing manner of constructing opening through gnomon.

Similar letters of reference indicate like parts.

The object of the equating solar chronometer embraced in this invention is to exhibit the mean or. clock time of day in lieu of the solar time; and the said chronometer consists of two semicircular arcs of brass or othersuitable metal or material, with an interior diameter of twelve or more or less inches each. These semicircular arcs are joggled and brazed together at a point midway between the two ends of each, so as to form right angles, with their inner surfaces flush with each other.

One (marked 'W a E in the drawings) of these semicircular arcs is supposed to represent the equator, and

is the time scale, its inner surface being divided into hours, and smaller divisionsor parts of the same, at the rate of fifteen degrees to the hour, commencing at six o'clock a. m. at its left or western" extremity, and ending at six oclock p. m. at the right or eastern extremity; this graduation or division being so modified as to countervail the slight deflection of the suns rays at the varying angles of obliquity, which deflection is greatest at sunrise and sunset, and least or reduced to nothing at twelve oolock m. The other semicircular are, marked B B in the drawings, is supposed to represent the meridian, and it supports a frame, 0 G, in which the gnomon D D is placed. This frame C C has ajournal at each end, which turns in a socket at the respective ends of the semicircles B B, and it has also a rectangular-shaped opening extending lengthwise through the middle, to be about seven inches in length and one and one-half inch wide, the inner edges havingledges on which the gnomon rests. The gnomon D I) is made of a plate of brass or other suitable metal or other material, withan opening, E E, through it equal in length to the distance betweenthe points corresponding with the sun's extremedeclination north and south. To project the form of the opening in the gnomon, first draw a line through the centre of the plate in the direction of its length, representing the meridian, marked N S, fig. 2. gross this line N S at right angles through its'centre by another, marked F F, fig. 2; the latter line, when the gnomon is in place, coinciding with the plane of the equator or time scale, fig. 1, W E. From the intersection of these lines mark on the meridian the degree of the suns declination north and south respectively,.observing that these two portions of the meridians are. tangents to a circle, fig. 2, gg, of six inches radius, and that the gradnations hf the degrees of declination north and south from the equator must be regulated accordingly. Now,-'oross the meridian at right angles by linesthrough the degrees thus marked on it, (or more frequently, if desired,)'and mark on thes'e lines, measuring from the meridian, the extent of the variation of the solar from the mean time at'the respective degrees of the suns declination. When it is fast/f the'variation' is marked to the left or Western side of the meridian, and when slow tothe eastern side. (The variation is-meafsured on a scale of fifteen degrees to the hour, the same as the time scalelf) Then connect the-points of variation thus markedby a line through the whole series. This line will form a figure somewhat resembling two slender pears of very unequal sizes connected at the stem ends; and this is the form of the said opening, fig. 2,'E E. cut outof the gnomon, through which the suns rays are admitted to the time-scale, and by which the shadow is thrown backward or forward just as much as the sun is'too fast or slow, thusalways showing the mean or clock time. A gnomon of another form may be made thus one plate of brass or other suitable metal or material, similar to the plate used for the previous gnomon: Draw a central'line representing the meridian, fig. 4, N S. To the surface of this plate transfer an exact copy of the figure tracedupon and cut out in the former gnomon. One half only of this figure is to be used. Thus from the point on the curved line at which the sun attains its extreme northern declination, which will be a little east of the meridian, fig. 4, N, trace strongly either of the lines which proceed thence to the point on said curved line a little west of'the meridian, fig. 4, S, at which the sun attains its greatest southern declination. On each side of this strongly-traced" line, and from end to end, out an opening, (fig- 4,

o o 0 0,) through the plate one-twentieth of an inch wide, leaving a space about one-thirtieth of an inch wide between them, through the middle of which runs the strongly-traced line aforesaid, fig. 4, N S. The portions of sunlight thrown through these openings widen so much in their passage to the time scale as almost to join each other, thereby reducing the shadow of the solid line between them to a sharply defined thread without penumbra. This thread coincides with thesaid strongly-traced line which is the true line of the gnomon. This gz'iomon, by reversing the position of itssurfaces, answers for the whole year: Thus, for the six months from the summer to the winter solstice,-turn that surface upward which throws the large curve westward of the meridian. Then for the six months from the winter to the summer solstice turn up the other surface, which turns the large curve eastward of the meridian. (This is gnom'on No. 2.) A gnomon of another form may be made thus, fig. 5: From a brass plate, prepared as for gnomon No. 2, out out a portion bounded by the said strongly'traced curved line on one side, and on the opposite side by a line parallel to the axis of the gnomon, leaving a margin of any width deemed-of sutficient strength for the purpose. This is gnomon No. 3, and will be used in the same manner as No. 2, both of them being what I call reversible gnomons. The axis common to all the gnomons diverges slightly from parallelism to the meridian. The equating solar chronometer must be set firmly on a permanent base, the plane of the semicircle representing the meridian being made .to coincide with the meridian of the place, and the gnomon being elevated to the latitude of the place. The timescale is suspend-ed by pivots or journals" about an inch below its east and west ends to the twoparts G and G. The lower edge of the semicircular meridian, N S, is widened in accordance with the segment of a circle whose centre is midway'on a line through the points of suspension. This segment h h passes between the jaws of the supporter H, in which there is a screw, K, to secure the gnomon in its adjustment to the proper degree in the scale marked on the side' of the semicircular meridian. When looking for the time of day the gnomon must be turned into such a position as will throw the widest light upon the time scale." The attainment of this position is shown when the shadow of the wire staplem, fig. 1, which is parallel to the meridian, coincides with the line drawn through its feet in the frame of the gnomon. During the six months from the summer to the win ter solstice the time is shown in the time scale, where it is crossed by the shadow of the line whose larger and southernmost portion runs on the west side of the meridian. The shadow of the other line, whose southernmost and larger portion runs on the east side of the meridian, shows the time during the six months from the winter to the summer solstice. It will be observed that the daily progress of the sun northward through one half of the year, and southward through'the other half, enables me to cross the time scale by the shadow of difi'erent portions of the gnomon from day to day, keeping pace continually with the progress of the variation from mean time, and as continually correcting it.

What Iclaiin as new, and desire to secure by Letters Patent, is-

A gnomon so formed as to throw the shadow backward when the sun is fast and forward when it is slow," to an extent equal in each case to its variation from mean or clock time, so that the shadow of the' gnomon will always cross the time scale at a point indicating meantime, substantially as described.

I also claim correcting the variation from'the mean or clock time by the use of the suns motion in his declination north and south. I

LLOYD MIFFLIN'.

Witnesses:

M. E. HACKER, J. H. MirrLIN. 

